1. Field of the Invention
This invention relates to a semiconductor light-emitting device, more particularly to a semiconductor light-emitting device having a function of diffusing light so as to enhance light extraction efficiency thereof.
2. Description of the Related Art
A conventional semiconductor light-emitting device usually uses light emitting diode(s) (LEDs) as a light source, and a fluorescent layer which includes fluorescent powders that are excited to emit light of a predetermined color when the LED is activated.
Currently, the fluorescent layer is normally applied to the semiconductor light-emitting device by a “conformal coating” method or a “remote phosphor” method. In the “conformal coating” method, the fluorescent layer containing fluorescent powders is disposed to surround the LED chip. In the “remote phosphor” method, the fluorescent layer is disposed above and is spaced apart from the LED chip. According to a paper by N. Narendran, Y. Gu, J. P. Freyssinier-Nova, and Y. Zhu, phys.stat.solidi (a) 202 (6), R60-R62, entitled, “Extracting phosphor-scattered photons to improve white LED efficiency”, since the fluorescent powders in the fluorescent layer function as point light sources, a large part of the light (about 60%) excited by the fluorescent powders would go back to and be absorbed by the LED chip. As disclosed in Taiwanese Patent no. 315528, the conventional LED chip is disposed on a trough-shaped reflector to reflect the light emitted from the LED chip. The semiconductor light-emitting device of the aforesaid patent is provided with a fluorescent layer using the “remote phosphor” method.
However, the aforesaid reflector can also focus the light emitted from the fluorescent layer on the LED chip, thereby resulting in absorption of the light reflected from the reflector by the LED chip, and in a decrease in the light extraction efficiency of the LED.
Moreover, since the surface of the aforesaid reflector is relatively smooth, an adhesion force between the reflector and an encapsulant that fills a space between the reflector and the LED chip is relatively weak, and moisture is likely to penetrate into the semiconductor light-emitting device, which has an adverse effect on performance of the semiconductor light-emitting device.
Therefore, it is important to improve the light extraction efficiency and the reliability of the semiconductor light-emitting device with the “remote phosphor” type fluorescent layer.